Advent of Code 2023 Day 2

Day 2, fortunately, proved easier than day 1. The puzzle gives results of draws of red, green, and blue items from bags. Part 1 asks to find which draws were possible given certain numbers of each item. Part 2 asks to find the minimum number of items to make each draw valid.

The computations proved trivial. Most of the challenge came in parsing the input, which looked like this:

Game 1: 3 blue, 4 red; 1 red, 2 green, 6 blue; 2 green
Game 2: 1 blue, 2 green; 3 green, 4 blue, 1 red; 1 green, 1 blue
Game 3: 8 green, 6 blue, 20 red; 5 blue, 4 red, 13 green; 5 green, 1 red
Game 4: 1 green, 3 red, 6 blue; 3 green, 6 red; 3 green, 15 blue, 14 red
Game 5: 6 red, 1 blue, 3 green; 2 blue, 1 red, 2 green

I used R for vectorized arithmetic. I ended up using several rounds of string splitting to extract the data:

parse_pairs <- function(pairs) {
    splits <- strsplit(pairs, " ") |> unlist()
    n <- length(splits)
    even <- seq(2, n, 2)
    # Since values come in value-color pairs
    result <- colors
    present <- splits[even]
    result[present] <- strtoi(splits[even - 1])
    result
}

parse_line <- function(line) {
    line <- sub("^Game \\d+:\\s+", "", line)
    # browser()
    draws <- strsplit(line, ";\\s+") |> unlist()
    pairs <- strsplit(draws, ",\\s+")
    lapply(pairs, parse_pairs) |>
        do.call(what = cbind)
}